A. Field of Invention
This invention relates to window treatment operating apparatus including a bi-directional drive, and, more particularly, to a cycloidal drive providing rotation of an output member in either direction at a predetermined mechanical advantage in response to rotation from an input member while resisting rotational forces from the output member. The input member is preferably a pulley operated by a beaded chain and the output member includes a sleeve supporting and rotating a mandrel of window treatment.
B. Description of the Prior Art
Roller shades are often used as window treatment and provide both a practical and an aesthetic function. Typically, a roller shade includes a tubular mandrel and a decorative panel wound on the mandrel. The mandrel can be selectively rotated by a user either in one direction or the other causing the panel to be either raised or lowered, depending on how it is wound on the mandrel. The roller shade is provided at its two ends with mounting means so that it can be mounted on a window frame or other similar location, using suitable brackets. Normally, one end of the roller shade is a simple rotatable coupling that allows the roller shade to rotate with respect to the bracket. The other end is provided with a bi-directional clutch that provides a mechanical advantage during the operation of the roller shade. Bi-directional clutch mechanisms of this type are disclosed in U.S. Pat. Nos. 4,433,765, 4,372,432 and 6,685,592, all incorporated herein by reference. These references disclose clutch mechanisms in which the mechanical advantage is developed between a pulley and a small shaft. One or more springs are also provided as a means for locking the mandrel to prevent undesirable rotation. Other clutch mechanisms are also known which are based on frictional braking. U.S. Pat. Nos. 3,135,369 and 3,920,106 also disclose bi-directional clutches useable for roller shades.
Recently there has been an increased need for roller shades having larger sizes and/or weights which in turn require stronger clutch mechanisms with a larger mechanical advantage, normally requiring more space. However, in the existing roller blinds, since mechanical advantage is dependent on the relative diameters of a pulley and a small shaft, and since the shaft has already been minimized, the mechanical advantage can be increased by increasing the size of the pulley. However, this is not a practical solution because space is too limited to accommodate a larger pulley, and in addition, a larger pulley may not be esthetically acceptable.
In addition, a stronger clutch mechanism requires more springs for locking the roller blind to prevent its undesirable rotation. However, more springs complicate the structure of the clutch mechanism, and increase the force required to operate the same.
U.S. Pat. No. 6,685,592, also incorporated herein by reference, discloses a clutch mechanism incorporating planetary gears as a means of developing a mechanical advantage. However, planetary gears require several parts that have to made with very precise dimensions. These gears are more expensive to make and assemble thereby adding significantly to the cost of the clutch. Furthermore the mechanical advantage obtainable with such mechanisms may not be sufficient for all purposes.
Many other window dressings, such as awnings, also rely on a rotating mechanism for activation.